The present invention relates to a rare earth magnet having a high electric resistance.
Inexpensive ferrite magnets have been extensively used as magnets used in a permanent magnet motor, and associated with miniaturization and advance of performance of an electric rotating machine, rare earth magnets having higher capability are increasing the using amount thereof. Representative examples of the rare earth magnets include a Sm—Co magnet and a Nd—Fe—B based magnet, and the performance and the cost thereof are being further improved.
However, rare earth magnets have a low electric resistance since it is a metallic magnet. Therefore, a motor having a rare earth magnet installed therein suffers such a problem in that the eddy current loss is increased to lower the efficiency of the motor. In view of such circumstances, various techniques have been proposed for increasing the electric resistance of the rare earth magnet itself to solve the problem.
For example, rare earth magnets having such a structure has been proposed that contain rare earth magnet particles bound with SiO2 and/or Al2O3 particles, as disclosed in Japanese Patent Provisional Publication No. 10-321427. The electric resistance of the rare earth magnet can be increased with SiO2 or Al2O3 intervening among the rare earth magnet. However, the magnet characteristics, such as the coercive force and the residual magnetization, are significantly lowered by adding SiO2 or Al2O3. It is accordingly difficult to be applied to motors of moderate to high power output.
According to the conventional techniques described in the foregoing, improvement of the electric resistance of the rare earth magnet can be attained, but it brings about significant deterioration in magnet characteristics.